Significant improvements in motor vehicle safety have derived and will expectedly derive in the future from the increased use of on-board radar systems and related data processing. Radar systems have been conceived as electromagnetic devices capable of detecting, locating and recognizing “target” objects, by transmitting electromagnetic signals and receiving back from these objects echoes which may be processed to identify location and/or other information.
In a radar receiver, the returning echoes received by an antenna (aerial) are amplified, down-converted and then passed through detector circuitry to extract e.g. the envelope of the signal (which may be referred to as the “video” or image signal). A video signal may be proportional to the strength (e.g. the power) of a received echo and may include, in addition to the desired echo signal, undesired power from internal receiver noise and external “clutter” and interference, which may degrade radar system performance significantly.
A good candidate for automotive safety is a Linear Frequency Modulated Continuous Wave (LFMCW) radar. This is a well understood and largely adopted radar concept which may provide the user with information about the target position (range and azimuth), velocity and amplitude. In various implementations, the basic LFMCW transmitted signal is a sequence of chirp waveforms centered at some specific frequency. A frequency considered for automotive applications may be e.g. 77 GHz.
Each chirp is a linear frequency modulated sine wave, with a modulation depth (o “bandwidth” BW) ranging e.g. from few MHz to several hundred MHz. The echo signal reflected back from the target may be mixed with the transmitted signal and an IF (Intermediate Frequency) signal generated. After e.g. amplification, band-limiting filtering and A/D conversion, the IF signal may be fed to a Digital Baseband processor where relevant information about the target behavior is extracted.
To ensure a correct censoring decision, the radar receiver may be designed to achieve a Constant False Alarm Rate (CFAR) and a maximum probability of detection. These points are particularly significant in safety applications in the automotive sector where the conventional designation “target” is indeed applied to persons (e.g. pedestrians) and objects (e.g. other vehicles, buildings, road fixtures) which are in fact intended to be avoided.
Various implementations of CFAR procedures are based on software approaches, mapped on powerful processors, e.g. based on a SIMD architecture. The complexity of certain processing procedures, combined with the speed constraints of radar systems for applications (with a short time between electromagnetic signal transmission and echo acquisition) aimed at detecting moving targets, may militate against the adoption of software approaches: CFAR procedures, such as e.g. Ordered Statistic CFAR (OS-CFAR), may be in fact be time absorbing, e.g. due to the amount of memory accesses, comparisons and concurrent sorting operations, in case of software implementation. These factors may end up by being an obstacle to the adoption of a radar-based system in the automotive sector, where cost may represent a significant factor.